1. Field of the Invention
The present invention relates generally to the field of data storage media, and more specifically to systems and methods for efficiently initializing, certifying or otherwise reading data from or writing data to such media.
2. Description of the Related Art
Disk drives are magnetic recording devices used for the storage of digital information. The digital information is recorded on substantially-concentric tracks on either surface of one or more magnetic recording disks. The disks are rotatably mounted on a spindle motor, and information is accessed by read/write heads mounted to actuator arms rotated by a voice coil motor. The voice coil motor rotates the pivoting arms and moves the heads radially over the surface of the disk or disks. During servowriting and/or initialization of a disk, the read/write heads must generally be accurately positioned on the disk to ensure proper reading and writing of servo information that will define the data storage tracks. After the servo writer writes the servo patterns on the disks, the control system is added to the hard drive assembly.
Movement of the pivoting arms is controlled by a servo system, which utilizes servo information recorded on one or more of the disks to center the head on a particular track. Servo information is utilized to determine an actual position of the heads. A voice coil motor (VCM) moves the heads if the actual head position deviates from a desired head location. Head position is typically controlled by a closed loop servo system.
The servo information in the servo tracks is often written with timing derived from a master clock track in the servo writing system. Writing of servo information must be precise. Servo information is typically recorded by special instruments containing precise mechanical positioners, positioned using highly accurate feedback devices such as optical encoders or laser interferometers.
A media servowriter is a device dedicated primarily to the servo data writing function. It can also perform other functions related to hard disk preparation for insertion into a hard disk drive. In operation, a media servowriter writes multiple disks in preparation for their placement in an HDD, with the goal being minimal further disk preparation once each disk is located in the HDD. Media servowriters can thus be housed in one location while hard disk assembly including completed disks may be performed at another location with the knowledge that the servowritten disks have been tested and approved for certain parameters.
Previously available servowriters suffer from a variety of shortcomings and system performance issues. An example of known system performance issues is that of system positioning accuracy: positioning heads over tracks to accurately read and write information at high speeds is an ongoing performance consideration that can always be improved or enhanced. Most, if not all, of the previously available systems suffer from an inability to support custom read/write heads, or provide accurate micro-move and settle times or track holding accuracy.
One particular problem with currently available disk drives and servowriters is the complexity associated with knowing the location of a head over a disk, and detecting and utilizing relative movements of disks, positioners, heads, and related equipment with respect to a reference point or plane. In current servowriters, no action occurs during normal operation to track or control disk or spindle position with respect to the drive base. Instead, the system tracks and controls head position with respect to some servowriter structural reference point, with the implicit assumption that disk position is sufficiently well known and stationary. In actual operation, however, the disks and spindle may shift, vibrate, deform, or otherwise alter their position in space with respect to the structural reference point. Current systems do not physically track disk position nor compensate for movement or irregularities resulting from real world conditions, including the aforementioned conditions and non-repeatable run out movement. A servowriter without the ability to track disk position and compensate for positional or movement irregularities may introduce or otherwise suffer from errors while heads are reading from or writing to the disks. This error introduction may limit the spin rate and/or track density of the disks.
It would be beneficial if one could track and compensate for media movement during the read and write process, thereby decreasing the risk of reading from or writing to incorrect locations on the media surface.
Another problem with currently available disk drives and servowriters is that of accurate head positioning. During the process of writing servo tracks on magnetic media, servo patterns must be positioned with high accuracy on different radial tracks. The traditional method of locating servo patterns on disks is to use a read/write head flying over a spinning media disk. The read/write head is attached to a rotary positioning device comprising a voice coil, associated voice coil motor, and a rotary optical encoder for closed loop positioning purposes. The rotary positioning device is used to hold the read/write head and swing the head over the spinning media disk. Errors in servo track accuracy can occur whenever the system does not maintain head position in a controlled radius as the media disk spins below the head. In certain circumstances the axis of the spinning media disk can translate laterally in the plane of rotation or the axis can wobble, tilting about a pivot point not coincidence with the media disk plane, thereby also translating the disk with respect to the head. Head position errors may also occur if the entire optical encoder fails to precisely track head position. The entire positioning device can translate or vibrate with respect to the spinning disk, or flexing of any components connecting the head to the optical encoder can produce positional errors.
Previous systems have employed a rigid mechanical connection between the optical encoder and the heads as well as a stable mechanical reference between the optical encoder and the axis of the spinning disk. In a disk having a track pitch below one micron, the rigid positional linkage performance between the optical encoder and the head as well as the optical encoder and spindle axis can be compromised by various factors, such as wobble or translation of the spindle axis within its bearing mount, causing radial runout. Other potentially problematic factors may include tiny distortions of the shape of any hardware that mechanically references the head to the spindle axis. External vibrations, vibrations from the spindle motor, temperature fluctuations or flutter from the disk can all contribute nanometer fluctuations and errors in positioning the head at constant track radius.
It would be beneficial to have a servo system that minimizes the dependence on the idealized mechanical references connecting spindle axis position to head position, thereby minimizing errors and fluctuations in the radius of servo data, or marks.
Another example of known system performance issues is that of system positioning accuracy: positioning heads over tracks to accurately read and write information at high speeds is an ongoing performance consideration that can always be improved or enhanced. One particular problem with currently available servowriters is the equipment used to format a disk writes a set of servo sectors to the disk, and the presence of relatively significant servo sector errors can cause the servowriter to indicate the disk is bad during verification testing. Alternately, when writing to a formatted disk, the presence of relatively significant errors in the servo sectors causes the disk drive to mark those sectors as unusable for data storage, either by detecting excessive servo errors while track following or excessive errors detected during data writing and reading, with the result that the data storage capacity of the disk would be reduced. Thus the downside of the old method of writing servo sectors or data sectors and monitoring the written data for errors would be discarded disks or unusable disk area. These drawbacks decrease yield and reduce available storage capacity.
It would be beneficial to have a method of writing data, including servo data, that would reduce the risk of decreased yields and/or storage capacity of hard disks as compared with previously known systems.
Furthermore, most, if not all, of the previously available systems suffer from an inability to support custom read/write heads, or provide accurate micro-move and settle times or track holding accuracy.
Disk drive heads are replaced periodically due to wear and tear. Instead of staking, wherein the head suspension and the head mount tab 3501 may suffer permanent deformation, it would be beneficial to offer a design that does not encounter permanent mechanical deformation during assembly or reassembly. In a particular hardware implementation, staking has required mounting a tab replacement or head arm or E-block after only two or three head replacements due to permanent deformation of the boss receiving bore of the head mount. It would be preferable to offer a design that can impart less distortion to the interface between the HGA and the mating head mount bore, increasing the number of reuses of the head mount tab before replacement is indicated.
Further, hard disk drives rely heavily on position reference information “written” or recorded as concentric bands of tracks onto disk surfaces. The operation of creating those tracks, known as servo track writing, requires precise record-phase head positioning and spindle mechanisms, as well as accurate timing and control electronics. The servo track writing process traditionally has been performed after disks have been installed into a “hard disk assembly”, or HDA. At the stage where disks are located in an HDA, the disks have been positioned on a spindle within the HDA. The HDA read-write heads have been loaded onto the disk or disks. An operator has traditionally placed the HDA onto a Servo Track Writer device that provides head positioning and servo pattern information to the HDA to enable proper recording of the servo tracks onto the disk or disks. This traditional technique is especially useful when multiple disks are used within the HDA.
However, as disk areal data density has increased, many Hard Disk Drives today utilize only one disk, decreasing the usefulness of the aforementioned technique. Further, increased areal data density is frequently accompanied by an increase in track density, which requires that the HDA write additional servo tracks. With at least two servo tracks for every data track, the number of servo tracks has increased at twice the rate of data tracks for a disk of fixed size or area. This increased number of tracks results in a dramatic increase in the time required to write the servo tracks. Servo writing, which previously took a few minutes can now easily exceed a half hour or more, depending on STW machine parameters, disk size, rotational speed (RPM), and total number of servo tracks. This time increase, coupled with the fact that many disk drives today use only a single disk, has created a demand for a media track writer, or MTW, that can simultaneously record servo tracks on multiple disks prior to installation into an HDA.
One aspect of the MTW that is particularly noteworthy is the mechanical clearance between the disk inside diameter, and the hub or chuck outside diameter, namely the disk opening and the hub that fills the opening. A significant clearance dimension is necessary to enable fast and reliable disk installation on and off the hub and to accommodate disk and hub manufacturing tolerances. If this clearance is too large, the disk or disks will move laterally and possibly axially during high RPM rotation. A finite clearance value exists under any set of dimensions. This clearance, if not addressed in some manner, creates an uncertainty with regard to the concentricity of servo tracks to disk ID, and can in certain circumstances result in significant eccentricity errors introduced when removing disks from the MTW and installed into a disk drive HAD. If uncontrolled, these errors can in certain circumstances exceed 4000 microinches, or millionths of an inch. Excessive eccentricity, or servo track “runout”, can cause servo capture and performance problems for the HDD, in that the head can be mislocated above the disk and can run outside a track, or begin in one track and end in another.
An additional aspect of a media servowriter is holding a hub, specifically a hub of a disk stacking cylinder employed to hold multiple disks during disk servowriting and certification. Previously available hub holding devices used some type of mechanical “jaws” that gripped the exterior of the hub and/or the notch formed between the hub and the main cylinder. The jaws were formed of some type of metal and were metal pieces used to pin the hub down and hold it in position by applying pressure to the upper side of the hub. These jaw-type locking devices tend to be imprecise in holding the hub or other cylindrical piece. At significantly high RPMs, such as in excess of 10,000 to 20,000 RPMs, centrifugal force works to pry these devices open, and many jaw type devices are pried open or move the piece as a result of high forces applied thereto. This prying tends to damage the hub and/or maintaining device and is generally unacceptable. Thus the previous devices could be characterized as easily pried open, with poor repeatability, and highly subject to movement of the piece.
It would be beneficial to provide a system overcoming these drawbacks present in previously known systems and provide an improved media servowriter, disk writer, and/or other device having improved functionality over devices exhibiting those negative aspects described herein.